[9.x] Improves Support\Collection reduce method type definition

src/Illuminate/Collections/Enumerable.php

@@ -805,7 +805,7 @@ public function random($number = null);
      * @template TReduceInitial
      * @template TReduceReturnType
      *
-     * @param  callable(TReduceInitial|TReduceReturnType, TValue): TReduceReturnType  $callback
+     * @param  callable(TReduceInitial|TReduceReturnType, TValue, TKey): TReduceReturnType  $callback
      * @param  TReduceInitial  $initial
      * @return TReduceReturnType
      */

src/Illuminate/Collections/Traits/EnumeratesValues.php

@@ -745,7 +745,7 @@ function ($carry, $callback) {
      * @template TReduceInitial
      * @template TReduceReturnType
      *
-     * @param  callable(TReduceInitial|TReduceReturnType, TValue): TReduceReturnType  $callback
+     * @param  callable(TReduceInitial|TReduceReturnType, TValue, TKey): TReduceReturnType  $callback
      * @param  TReduceInitial  $initial
      * @return TReduceReturnType
      */

types/Support/Collection.php

@@ -634,6 +634,14 @@ function ($collection, $count) {
         assertType('User', $user);
         assertType('int', $int);
 
+        return 1;
+    }, 0));
+assertType('int', $collection
+    ->reduce(function ($int, $user, $key) {
+        assertType('User', $user);
+        assertType('int', $int);
+        assertType('int', $key);
+
         return 1;
     }, 0));